The semiconductor industry has experienced rapid growth due to improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from shrinking the semiconductor process node (e.g., shrink the process node towards the sub-20 nm node). As the demand for miniaturization, higher speed and greater bandwidth, as well as lower power consumption and latency has grown recently, there has grown a need for smaller and more creative packaging techniques of semiconductor dies.
As semiconductor technologies further advance, package-on-package semiconductor devices have emerged as an effective alternative to further reduce the physical size of a semiconductor device. In a package on package semiconductor device, active circuits such as logic, memory, processor circuits and the like are fabricated on different wafers and packages. Two or more packages are installed on top of one another, i.e. stacked, with a standard interface to route signals between them. Much higher density can be achieved by employing package on package semiconductor devices. Furthermore, package on package semiconductor devices can achieve smaller form factors, cost-effectiveness, increased performance and lower power consumption.
The standard interface of a package-on-package semiconductor device may comprise a plurality of bumps such as ball grid array (BGA) balls. The bumps provide electrical conductive paths between different wafers and packages. In addition, the bumps also provide addition mechanical support for the stacked packages.
The bumps are susceptible to failures caused by stresses. In order to prevent the bump failures, underfill layers may be used to protect the bumps. More particularly, the underfill layers formed between different wafers and packages are used to increase the reliability of the stacked packages by reducing stresses on the bumps. The underfill layer may be formed by a capillary dispensing method, where liquid underfill material flows beneath the packages by capillary action.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale